The present invention relates to an arrangement for generating a triggering signal for a safety device in a motor vehicle in response to a rollover process, provision being made for a first arrangement, which derives a first decision criterion for the triggering of a safety device in the motor vehicle from the turning rate measured at least for the longitudinal axis of the motor vehicle and/or from the accelerations measured at least in the direction of the transverse axis and the vertical axis of the motor vehicle. A previously proposed arrangement for generating a trigging signal for a motor vehicle safety device is described in German Published Patent Application No. 196 09 176 A1.
In the event that a motor vehicle experiences a rollover, all of the passenger protective devices installed in the vehicle must be triggered in a timely fashion, including, for example, roll bar, seat-belt tensioner, front and side airbags, etc. For all of these protective devices to be triggered in a timely fashion, it is important to detect as early as possible whether the turning motions of the vehicle about its longitudinal axis, its transverse axis, or its vertical axis are going to lead to a rollover. As a rule, rollover processes occur about the longitudinal axis of the motor vehicle, turning motions of the vehicle about its vertical axis and its transverse axis occurring only seldom. The safety devices in the vehicle also should be actually triggered only when a rollover is in fact occurring to the vehicle.
European Published Patent Application No. 0 430 813 depicts an arrangement, discussed above, for generating a triggering signal for a safety device in response to a rollover process of a motor vehicle. For detecting various rollover processes of a vehicle, the output signals of a turning rate sensor and of three acceleration sensors are evaluated. In order to be able to detect various types of rollover situations, provision is made for a plurality of combinations of the four sensor signals. The triggering signals yielded from the various sensor signal evaluations are fed here to an OR gate, which, if one of the possible triggering signals is applied at its inputs, conveys a triggering command to a triggering device for a roll bar or other safety devices.
In the event of a lateral impact of the vehicle with a low obstacle, e.g., a curb, the vehicle suffers a quite powerful tilting motion, leading to a rollover. It is thus an object of the present invention to indicate an arrangement capable of detecting a rollover process of a vehicle, in a timely fashion and with great reliability.
The aforementioned objective is achieved in that a circuit arrangement generates a triggering signal if the turning rate about the longitudinal axis and the acceleration in the direction of the transverse axis both exceed a threshold value at the same time, the threshold value for the turning rate and the threshold value for the acceleration being selected such that the safety device is triggered in response to a lateral impact of the vehicle with a low obstaclexe2x80x94e.g., a curb.
It is advantageous to bring into consideration a second decision criterion. For this purpose, in parallel to the threshold value decisions for the turning rate about the longitudinal axis and the acceleration in the direction of the transverse axis, the circuit arrangement carries out a second threshold value decision regarding the acceleration in the direction of the transverse axis, the second threshold value decision being based on a different acceleration threshold value than the first threshold value decision. The parallel branch, as soon as the other acceleration threshold value has been exceeded for a preselected time duration, decides for triggering the safety device, and the circuit arrangement emits the triggering signal only when the decision for triggering has been made in both circuit branches at the same time.
In accordance therewith, the second decision criterion can be derived from the turning rate and/or the accelerations using measuring signals that are different from those measuring signals used for the derivation of the first decision criterion. The second arrangement also can derive the second decision criterion from the measuring signals of the turning rate and/or of the accelerations in accordance with a different algorithm than that used by the first arrangement for the first decision criterion.
Advantageously, the first arrangement, from the measured turning rates about all three vehicle axes, determines the position of a vehicle-fixed point projected onto a horizontal plane, and, if the projected point goes beyond the limits of a vehicle-fixed surface, also projected onto the horizontal plane, the first arrangement decides for triggering the safety device. Parallel to this, the first arrangement can calculate the rotational energy of the vehicle from the measured turning rates about all three vehicle axes, and it decides for triggering the safety device if the rotational energy exceeds a threshold value. This procedure is particularly effective if the safety device is to be triggered as quickly as possible.
To ensure that an offset error of the turning rate sensors does not lead to an erroneous decision due to temperature or age, an integration of the measured turning rates, resulting in a tilt angle and a pitch angle of the vehicle for deriving the first decision criterion, is only started if the value for the turning rate exceeds a minimum value.
The second arrangement, advantageously, is designed so that it calculates the tilt angle from the measured accelerations in the direction of the vertical axis and in the direction of the transverse axis and/or it calculates the pitch angle from the measured accelerations in the direction of the vertical axis and in the direction of the longitudinal axis, and that, if the tilt angle or the pitch angle exceeds a threshold value, it decides for triggering the safety device. The second arrangement can also execute a threshold value decision regarding the value of the measured acceleration in the direction of the vertical axis, and, if the acceleration exceeds, for example, 0.2 times the value of gravitational acceleration, it can decide for triggering the safety device. Thus it is assured that if the vehicle finds itself in a weightless state through lifting off from the ground, the second decision criterion is derived.
The safety device in the vehicle should also be triggered if the vehicle experiences a lateral impact with a low obstacle, for example a curb, without its leading necessarily to a rollover. For this purpose, provision is made for a circuit arrangement that generates a triggering signal if the turning rate about the longitudinal axis and the acceleration of the vehicle in the direction of the transverse axis both simultaneously exceed a threshold value. In order to exclude the possibility of an erroneous decision here also, it is advantageous not to stop at this one decision criterion, but rather to consult a further decision criterion. For this purpose, parallel to the threshold value decisions regarding the turning rate about the longitudinal axis o and regarding the acceleration in the direction of the transverse axis, the circuit arrangement carries out a second threshold value decision with respect to the acceleration in the direction of the transverse axis, the second threshold value decision being based on a different acceleration threshold value than the first threshold value decision. The parallel branch, as soon as the other acceleration threshold value has been exceeded for a predetermined amount of time, decides for triggering the safety device, and the circuit arrangement only emits the triggering signal if the decision has been made simultaneously in both circuit branches for triggering.